船用中厚板焊缝特征导波传播理论和缺陷反演及表征机理研究

The health of the weld of thick steel plates is extremely important to the structural reliability and service security of the offshore platforms. Here, a new inspection theory and Characterization method for the welding defects of medium and thick ship steel welds is advanced based on a new feature-guided wave, weld-guided wave SHwn, and all the key problems are researched in this project on the propagation characteristics, the interaction relationships among the wave mode, the welding parameters and the defects, the feature extraction, optimization and inversion of the signal, as well as the inversion, identification and characterization of the welding defects. The propogation characteristics and dispersion equation of SHwn will be derived starting with the theoretical solution of the wave equation, to explore the relationships between the wave modes of SHwn and the structural, material and welding technique of the welds, so as to establish a optimum wave-mode selection mechanism. Through the study of the reflection coefficient, the refraction coefficient, the displacement and the energy change of the wave, the effect dicipline between the echo and typical welding defects will be researched combining theoratical derivation and numerical analysis. Precision location algorithm will be studied according to exploring the scattering mechanism of SHwn around the defects based on Decomposition of The Time Reversal Operator (DORT) method. Furthermore, the time-domain and frequency-domain characteristics will be studied to investigate effective feature extraction and optimization algorithm, so as to establish the relationships between the features and defect types, and between the feature variables and defect variables, to realize the inversion,identification and characterization of the defects. All the research results will provide a new theory and technological support for the evaluation for the security and reliability of the ships and offshore structures.

船用中厚板焊缝健康状况对海洋结构可靠度和服役安全度至关重要。项目以长距离船用中厚板焊缝为研究对象，提出基于焊缝特征导波的焊缝缺陷检测理论与表征新方法。项目围绕焊缝特征导波SHwn传播特性、对典型焊缝缺陷的灵敏性、与焊缝缺陷的相互作用、以及SHwn信号的特征提取、优化与缺陷的反演与表征机理等科学问题展开研究。从波动方程的理论求解入手，研究SHwn传播特性和频散方程，探索SHwn各模态与焊缝结构、材质、工艺之间的相互关系，建立最佳模态选择机制；从反折射系数、位移和能量变化等多角度着手，研究典型焊缝缺陷对回波的影响规律；基于时间反转算子分解法研究焊缝特征导波对于缺陷的散射机制，探求焊缝缺陷的精确定位算法；研究缺陷回波的时频域特性，探索有效的特征提取及优化算法，建立特征—缺陷类型、特征量—缺陷大小的映射关系，实现焊缝缺陷的识别和表征，为掌握海洋结构安全性和可靠性评估提供新的理论和技术支撑。

船用中厚板焊缝健康状况对海洋结构可靠度和服役安全度至关重要。项目以长距离船用中厚板焊缝为研究对象，提出基于焊缝特征导波的焊缝缺陷检测理论与表征新方法。项目利用近场动力学理论，从理论上系统研究了SH模态特征导波的传播特性。通过折射点处物质点上力和位移的连续性获得SH波的折射和反射特性，结合焊缝表面附近虚拟边界层上的受力情况研究，得出焊缝中SH模态特征导波的频散方程。利用近场动力学数值模拟方法，结合有限元二维、三维建模和仿真分析方法，分别研究了对接焊缝余高、宽度及泊松比等焊缝结构和材料参数对焊缝中两种基本特征导波模态（Sw0模态和SHw0模态）传播规律的影响。在此基础上，从理论和模拟仿真两个方面，分别研究了Sw0模态和SHw0模态特征导波在不同焊缝缺陷处的散射情况以及与不同焊缝缺陷的相互作用，分析了缺陷回波波形与缺陷类型的关系。研究表明，根据SHw0模态与缺陷作用后散射场的断裂程度与非对称性，可以分别判断焊缝中孔洞缺陷的严重程度和裂纹所在位置。系统分析了焊缝特征导波回波信号的基本特点，提出了基于稀疏表示的回波信号处理方法，构造了适应特征导波信号特点的过完备Morlet小波基原子字典。提出利用分裂増广拉格朗日收缩算法求解稀疏表示向量的目标函数，实现了回波信号中各成分的稀疏表示和缺陷信号的特征识别与定位。提出了结合PCA与SVM的焊缝缺陷分类方法，实现了典型焊缝缺陷的有效分类。在理论研究的基础上，针对焊缝表明曲面和不平整的特点，创新性地提出了基于特征导波的焊缝缺陷检测压电阵列式柔性传感器，完成了传感器的设计、加工和性能检测，并利用相控阵技术，研究了阵列传感器的信号聚焦，实现了多信号的相位无混叠、幅值线性叠加。项目已发表论文23篇（SCI10篇，EI3篇），申请发明专利11件，授权2件，培养博士2名，硕士生8人，国际会议交流5人次，获省部奖二等奖1项。